Ultrasonic transducer for intruder alarm system

ABSTRACT

An ultrasonic/electrical transducer for operation at a given frequency in an ultrasonic intruder alarm system is provided with a shallow self-supporting dish-shaped radiator mounted at the center of its concave surface to one face of a piezoelectric ceramic crystal. The opposite face of the crystal is secured to one end of a tuning stub which extends one-half wavelength from the center of the radiator and is connected at its midpoint to a base through an accoustic isolator. The stub is tuned by addition of trimming washes to its free end. The crystal is of the expansion/compression type having its piezoelectric axis parallel to that of the tuning stub and perpendicular to the surface of the radiator. The base is made of two parts joined by means which are the structurally weakest point of the assembly so that, if the transducer is tampered with, this point will move tripping a tamper switch to signal the alarm.

immiwfi @MWS Patent 1 Antonio 5] June 5 973 [54] ULTRASUNHC TRANSDUQERFOR 2,922,999 1 1966 Carlin ..340/15 HNTRUDER ALARM SYSTEM 3,296,5861/1967 Midlock et al. ..340 15 [75] Inventor: ,llohn Antonio,liairfield, Conn. Primary Examiner l D Miller [73] Assignee: The MoslerSafe Company, Hamil- Assistant ExaminerMark O. Budd 1011,0hi0 tggr ngy-James s. Hight, Herbert C. Brinkman Jr., 22 Filed: 1 61. 2a, 1972 pp N91229,995 57 ABSTRACT An ultrasonic/electrical transducer for operation ata [52] US. Cl. ..3l0/8.2, 179/110 A, 3 l0/8.3, given f q y in anultrasonic intruder alarm System 310/8.7, 3l0/9.1, 3l0/8.l, 340/8 MM, isprovided with a shallow self-supporting dish-shaped 340/15 radiatormounted at the center of its concave surface to one face of apiezoelectric ceramic crystal. The p 1 8 posite face of the crystal issecured to one end of a 8 9 1 tuning stub which extends one-halfwavelength from the center of the radiator and is connected at itsmidpoint to a base through an accoustic isolator. The stub [56]References Cited is tuned by addition of trimming washes to its freeUNITED STATES PATENTS end. The crystal is of the expansion/compressiontype having its piezoelectric axis parallel to that of the tun-1,802,781 4 1931 Sawyer et al. ..340 10 mg Stub and perpendicular to theSurface of the radia 3,675,053 7/1972 M1fune ..3l0/8.2 2,800,647 7 1957Baerwald.... .....310 s.2 x The base 18 ad f two parts jOll'led by means3,287,693 11/1966 Bango i ..340 15 which are the structurally Weakest Pof the 3,5l7,226 6/1970 Jones, Sr. ,.3l0/9.1 Sembly so that, if thetransducer is tampered with, this 3,218,488 3 189KB 9 --3l0/8- pointwill move tripping a tamper switch to signal the 3,210,724 10 1 65 Joneseta ....340/8 MM alarm 2,345,472 3/1944 Goldsmith ..340/15 15 Claims, 4Drawing Figures PATENTEE M 5 I973 SHEET 2 [1F 2 ULTRASQNTC TRANSDUCERFOR HNTRUDER ALARM SYSTEM The present invention relates to ultrasonictransducers of the type which are used with ultrasonic frequencyelectrical transmitters and receivers to transmit and receive ultrasonicwave energy through air. More particularly, the present inventionrelates to such transducers which are specifically useful withultrasonic space alarm systems which are designed to detect the presenceof intruders in certain rooms or enclosures.

Space alarm systems are those which protect an area or enclosure againstintruders by detecting the presence or motion of an intruder within thearea. This detection is achieved by filling the area with radiatedenergy and measuring disturbances in the reflected energy caused by theintruders. This energy is usually in one of two forms, eitherelectromagnetic or ultrasonic. Most frequently, detection is achieved bysensing a doppler frequency shift in energy reflected from movingobjects within the enclosure. The present invention is primarilyintended to improve upon space alarm systems of the ultrasonic type byproviding a more effective transmitting and receiving transducer forsuch applications.

Ultrasonic space alarm systems usually employ ultrasonic continuous waveenergy at a frequency just above the audible frequency range atapproximately 20 kilohertz. These transducers are either driven bytransmitters which generate ultrasonic frequency electrical signals ordrive receivers to produce electrical signals. Normally, one transduceris used for transmitting and another is used for receiving, although insome applications a single transducer can be used for both purposes.Some transducers employ magnetostrictive devices, while others employpiezoelectric ceramic crystals. The present invention relates totransducers of the piezoelectric type. Such transducers are disclosed inthe prior art in Bango US. Pat. No. 3,287,693. The transducer of Bagnoemploys a deep parabolic bell-shaped diaphragm supported by elasticmounts at its edges to a base. The center of the diaphragm has affixedto it a piezoelectric ceramic crystal which bends when excited byelectrical energy to induce standing wave undulations in the diaphragm.This transducer is not particularly efficient and tends generally tohave a broad band characteristic.

In space alarm system applications, it is desirable that the transducersemployed have a generally omnidirectional pattern so that the room orenclosure may be filled with relatively uniform strength radiation.These transducers are normally mounted in the ceiling of the room sothat the radiation will propagate in more or less uninterrupted pathsthroughout the room. It is a further desirable feature of suchtransducers that they have a generally high efficiency so that, intransmitting applications, less power is required to drive them, andsecondly, in receiver applications, so that a stronger signal can bederived to be supplied to the receiver for detection.

Most space alarm systems operate on a doppler principle. For suchdoppler systems it is desirable to radiate only a single frequency ofenergy, and for this purpose, the most desirable transducer is one whichhas a narrow radiation band. It is further desirable that suchtransducers be provided with a rugged and sturdy mounting, one whichwill allow a long reliable life of the transducer, which will enablecontinued high efficiency operation, and which will allow the additionof simple means to detect tampering with the transducer. It is generallyan objective of the present invention to provide a transducer which hassuch features and results in generally greatly improved operation overdevices of the prior art provided for this purpose.

Accordingly, the present invention is predicated in part upon theconcept of providing an ultrasonic transducer having a generallyself-supporting shallow dish radiator which is mounted at its center,through a piezoelectric crystal, to a base. The present invention isfurther predicated in part upon the concept of providing such atransducer with a tuning stub, and more particularly, with a stub whichoperates to provide high efficiency narrow band operation of thetransducer and, further, which operates as a mounting means for thecrystal which supports the radiator.

More specifically, the radiator is generally of a shallow dish shapehaving one fae of a piezoelectric crystal tirmlysecured to the center ofthe concave surface of the radiator. The radiator is self-supportingwhen mounted at its center, rather than of the diaphragm type which issupported at its edge as are common loudspeaker cones and transducers ofthe Bagno type. The crystal has its piezoelectric axis perpendicular tothe surface of the radiator at the point to which it is attached. Theface of the crystal opposite the radiator is secured to one end of aone-half wavelength rod which serves as the tuning stub. Means areprovided for securing washers to the free end of the stub to facilitatein trimming the stub to the proper resonant frequency. The transducer,when driven by electrical energy, will expand and contract in thedirection of its axis to displace the radiator at its center in relationto the tuning rod. These oscillations will propagate along the rod andreinforce the motion of the crystal at the proper resonant frequency.The mounting of the resonator and crystal is achieved by securing themidpoint of the tuning stub through an accoustic isolator to a rigidbase. This midpoint will be essentially an accoustic null point on thetuning stub, and mounting at this point will least affect the efficiencyof the transducer and the narrowness of the band at which it is designedto operate.

Furthermore, the base is designed in two parts which are joined in amanner which is less structurally strong than the mounting between thetuning rod and the base so that if there is any tampering with thetransducer the base will separate into two parts. At the two parts, atamper switch is provided which will signal any parting of thisconnection. In this manner, tampering can be detected without the needto additionally connect any components to the head portion of thetransducer which comprises the radiator, crystal and tuning stub. Suchconnections will interfere with the general narrow band operation of thetransducer and generally adversely affect the efficiency of thetransducer unless extensive design compromises are made to accommodatethem.

These and other objectives and advantages of the present invention willbe more readily apparent from the following detailed description of thedrawings illustrating one preferred form of an ultrasonic transmittingand/or receiving transducer suitable for use in ultrasonic space alarmsystems and generally embodying the principles of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS FIG. l is a diagrammaticperspective view illustrating an ultrasonic alarm system for protectionof a room or enclosure, the alarm system utilizing ultrasonictransducers according to principles of the present invention.

FIG. 2 is a cross-sectional view of the ultrasonic transducers of FIG.1.

FIG. 3 is a horizontal cross-sectional view of an ultrasonic transducerof the present invention taken along line 33 of FIG. 2.

FIG. 4 is a horizontal cross-sectional view similar to FIG. 3, but ofreduced scale, of an ultrasonic transducer of the present inventiontaken along line 4--4 of FIG.

Referring to FIG. I, a simplified diagrammatic representation of anultrasonic alarm system is illustrated. Such a system is disclosed in myco-pending application Ser. No. 110,735 filed Jan. 28, 1971.

This alarm system is illustrated in FIG. 1 as protecting a room orenclosure by radiating ultrasonic energy at a given frequency into theenclosure through a transmitting transducer 11. This energy is reflectedfrom the enclosure 10 and received by a receiving transducer 12. If anobject such as an intruder is moving within the enclosure 10, a dopplerfrequency shift will occur in the received signal which is detected togenerate an alarm signal. Both transducers l1 and 12 are preferablymounted in the ceiling of the enclosure.

The alarm system generally includes an ultrasonic transmitter 21 whichhas an output connected to the transmitting transducer 11. The system isfurther provided with an ultrasonic receiver 22 which has its inputconnected from the receiving ultrasonic transducer 12. A detector 23 isprovided having a pair of inputs connected one to the output of thetransmitter 21 and another from the output of the receiver 22. Thedetector detects the doppler frequency shift by comparing the receivedsignal with the transmitted signal to generate a detected signalrepresentative of the doppler frequency component of the received signalwhich is supplied through the logic circuit 24 to trigger an alarm 25.

The transducers l1 and 12, according to the present invention, aresubstantially identical and can be better understood by reference toFIG. 2.

The preferred embodiment of a transducer according to the presentinvention includes two basic parts, the ultrasonic head assembly 31, andthe transducer base 32 which mounts the head assembly 31 to the closurestructure as, for example, the ceiling of a room.

The base 32 includes a cylindrical plastic shell tube 34. The shell tube34 is provided with a pair of annular grooves 35 and 36 on the interiorsurface thereof and near the upper end of the tube 34. The shell tube 34is connected to a mounting pan assembly 38 by a threepoint spider-likesupport arrangement at the uppermost groove 36. This spider-like supportarrangement includes a pair of pins 39 and a set screw 40 each extendingradially outward from the mounting pan side wall and spaced thereaboutat approxamately 120 intervals. This mounting arrangement can be betterunderstood by reference to FIG. 3 which illustrates the vertical sidewall portion of the mounting pan 38, the pins 39 extending radiallytherefrom and riding in the groove 36 in the inner wall of the tube 34,and the set screw 40 extending radially from the side wall of the pan 33and through an opening in the wall of the tube 34 at the groove 36therein. The set screw is provided with a pair of elastic stop nuts 41and 42 which tighten screw 40 with respect to the walls of the mountingpan 38 and the shell tube 34, respectively.

A dust cover plate 45 underlies the mounting pan assembly 38 (FIG. 2) ata point immediately above a groove 35. The lower surface of this plate45 is covered with a pad damper 46. The dust cover 45 is mounted to achassis 48 at upper flange portions 49 thereof by a pair of screws 50.The flange portion 49 of the chassis 48 is square in shape (FIG. 4), andis mounted to the tube 34 by its corners which are positioned in thelower groove 35. At the lower end of the chassis 411, in the centerthereof, is provided a mounting hole 55 at which the transducer headassembly 31 is supported in a man ner which will be more completelydescribed below. A tamper switch 61 is mounted to the dust cover 45 byway of a tamper switch bracket 62. A switch actuator 63 projects throughthe bracket 62 to contact the undersurface of the mounting pan assembly33. The switch circuit, illustrated diagrammatically in FIG. 2 is madeto be in a normally open or closed condition when the actuator 63 isdepressed as indicated in the Figure, and to change to the oppositecondition in the event that the actuator is allowed to extend, which isthe case which will occur if someone attempts to tamper with thetransducer to disable it. The circuit connectors 67 connect the tamperswitch to an alarm cir cuit which will sound an alarm if tamperingoccurs.

The transducer may be mounted either against the ceiling through screws69 extending through the mounting pan assembly 38 into the ceiling asindicated by the reference line 71 in FIG. 2. Alternatively, thetransducer may be flush mounted against the ceiling by use of a bezel 72having an adhesive backing 73. In such a case, the tube 34 is insertedinto the hole in the ceiling from approximately the same or slightlylarger diameter as the tube 34 so that it rests against the celling whenthe position indicated by the line 74 in FIG. 2. The transducer issecured tightly to the ceiling by a mounting strap 75 which tightensabout the tube 34.

As will be apparent from the description below, the transducer head 31is mounted more securely to the chassis 43 than is the chassis 48 to theshell tube 34, or for that matter than is the shell tube 34 to themounting pan 38. Thus, any attempt to disable the transducer by removingthe head 31 will cause a clislodging of the chassis 48 with respect tothe mounting structure which is stationary with respect to the ceiling.This will cause the dust cover to move with the bracket chassis to movethe tamper switch 61 with its actuator 63 away from the mounting pan 38causing the switch 61 to actuate giving a tamper alarm. For example, ifthe trans ducer assembly is mounted against the ceiling represented byline 71, the spider mounting. legs 39 will yield first causing theentire tube 34 and head assembly portion 31 to move away from themounting plate 33 actuating the tamper switch which will be carried withit. Normally, when this mounting only method is contemplated, thechassis 48 is more securely constrained to the groove 35. On the otherhand, if the transducer head assembly is mounted flush with the ceilingrepresented by line 74 in FIG. 2, the tube 34 will be rela tivelysecurely constrained to the ceiling. If an attempt is made to remove thechassis 48, it will dislodge from the groove 35 carrying with it thetamper switch at which will move away from the mounting pan 33 which isconnected to the tube 34. This will also actuate the tamper switchalarm. For this mounting method, the chassis 48 may be less stronglyconstrained in the groove 48.

The transducer head assembly 31 includes a piezoelectric crystal 81mounted with its axis oriented vertically. Electrode faces 82 and 83 atthe upper and lower ends of the crystal 81 connect through leads 84either to the output of a transmitter or to the input of a receiver. Thecrystal 81 will expand and contract in the direction of its verticalaxis when signals are applied to the leads 84 when used with atransmitter, or alternatively, will generate electrical signals on theleads 84 when caused to expand or contract in the vertical directionwhen used with a receiver. A suitable crystal 8] is the Gulton Model M-3D8 HDT 31.

An upwardly concave shallow aluminum dish 86 having an outside diametersomewhat less than the inside diameter of the tube 34 is situated at thelower end of the crystal 81. Through the center of the dish 86 isconnected a circular, thin aluminum slug 87 which is secured to the dish86 by nonconductive epoxy cement. The electrode face 83 of the crystal81 is secured to the center of the slug 87 also by epoxy cement.Suitable epoxy cement for this purpose is the Emerson & Cummings ResinNo. 2850 FT used with their No. 9 catalyst hardener. The electrode face82 at the upper end of the crystal 81 is similarly secured by the sameepoxy cement to a cylindrical aluminum resonator rod 88. The resonatorrod extends upwardly through the hole 55 in the bracket 48. Thetransducer head assembly 31 is secured to the base 52 at this hole inthe bracket 48 by means of a rubber grommet 89 which electrically andaccoustically isolates the rod 88 from the bracket 48. The grommet isconnected to the respective rod 88 and chassis 48 by a synthetic rubberadhesive sealant 90, such as Dow Cornings SILASTIC RTV 891. The rod 88is connected to the chassis 48 at an accoustic node or null point whichis approximately half the distance from the lowermost surface of thedish 86 to the uppermost tip of the rod 88. This midpoint isapproximately onequarter of an accoustic wavelength (speed of soundwithin the rod 88) from either end of the transducer head assembly 31.The rod 88 engaged in this manner serves as an accoustic band passfilter tuned to the midban frequency at which the transducer is to beoperated. The rod 88 is manufactured slightly less than the desiredlength and trimming washers 92 are added to the upper end of the rod 88during tuning of the transducer head. The washers 92 are secured to theupper end of the rod by a stainless steel screw 93.

The preferred frequency for space alarm applications has been selectedat 22 kilohertz. At such frequency, certain dimensions of the transducerhead have been found desirable. The preferred length for the rod 88,including the crystal 8], is about 3.838 inches measured from the lowersurface of the dish 86 to the upper end of the rod 88 beneath thetrimming washer. Washers are provided of aluminum in thicknesses of.010, .020, .030, and .050 inches. This has been found quite suitablefor trimming the rod 88 to resonate at the desired frequency in thatproduction of the rod can be easily held to .015 inches tolerance andsome allowance is still present for other variations in an assembly. Thediameter of the rod is selected at one-half inch. The distance from thelower surface of the dish 86 to the center line of the chassis 48 at themounting hole 55 for the rod 88 is suitable 1.98 inches. The diameter ofthe dish 86 is suitably 3.91 inches clearing the inside diameter of thetube 34 by roughly one-eighth of an inch on all sides.

Certain electrical circuit components are provided in the transducerassembly. These are mounted by a printed circuit board 94 to the chassis48 through screws 95 and spacer washers 96. A transformer 97 is alsosecured to the chassis 48. Transformer 97 serves as an impedancematching transformer for the crystal 81 and the printed circuit board 94carries appropriate terminals and, when the transducer is used with areceiver, carries a preamplifier circuit. A schematic of this circuitappears in the lower right-hand corner of FIG. 2. When the transducer isused as a transmitter, the transformer 97 schematically represented bywindings 97A is merely connected between the leads 84 and the output ofthe transmitter 21. The transmitter has approximately 35 to l step-upratio with this purpose. The impedance levels at the input is 50 ohmsand at the output 62.5 K ohms. The transformer 97 is used in the sameorientation in the receiving application, however, a preamplifier 98 isconnected between the crystal 81 and the transformer winding 97A withthe high impedance winding of the transformer 97 connected to theamplifier output and the preamplifier inputs connected across leads 84.

The transducer described above'in detail thus provides a rugged,efficient device for use with an ultrasonic intruder alarm system forboth transmitting and receiving. The transducer head, when constructedin accordance with the dimensions described in relation to thewavelength selected, and the specific relation to the base constituteonly a preferred form of the general concepts of the present invention,but this preferred form has considerable improved performance overdevices of the prior art particularly when used in alarm systems of thistype. It will be appreciated that this and other forms of the inventioncan also greatly improve performance of not only alarm systems but othertypes of systems in which transducers are generally employed.

What is claimed is:

1. An ultrasonic transducer comprising:

a piezoelectric crystal having first and second electrode faces onopposite sides thereof;

a self-supporting shallow dish radiator mounted at its center to thefirst face of said crystal to be solely supported thereby; 1

a support member mounted at one end to the second face of said crystaland having its other end structurally unconnected;

a base; and

a connecting element secured between said support member at anacoustical node in said support member and said base.

2. The transducer of claim 1 wherein:

said connecting element includes an ultrasonic acoustic isolator.

3. The transducer of claim 1 additionally including:

an electrical switch having alternately conducting and nonconductingstates mounted on one of said base or said support member and having anactuator contacting the other of said base or support member forchanging between said states when said support member and said base moverelative to each other, thereby providing a tamper detection means.

4. A transducer according to calim 1 for operation at a given ultrasonicfrequency wherein:

said support member comprises a tuning stub con- 5 nected at one end tosaid second face and aligned perpendicular to said second face, saidstub being approximately one half the wavelength in said stub of anacoustical wave at said given frequency, and said stub being connectedto said base at the midpoint thereof.

5. The transducer of claim 1 wherein:

said radiator has a curved shape presenting one concave and one convexsurface; and

said radiator is mounted to said crystal at the center of said concavesurface.

6. The transducer of claim 1 further comprising:

an impedance transformer mounted to said base having first and secondwindings, the leads of said first winding being connected to theelectrode faces of said crystal and the leads of said second windingbeing connectable across the outputs of an ultrasonic frequencytransmitter.

7. The transducer of claim 1 further comprising:

a preamplifier having inputs connected across the electrode faces ofsaid crystal; and

an impedance transformer mounted to said base having first and secondwindings, the leads of said first winding being connected to the outputof said preamplifier and the leads of said second winding beingconnectable across the inputs of an ultrasonic frequency receiver.

8. The transducer of claim 1 wherein:

said crystal has its piezoelectric axis oriented perpendicular to saidradiator.

9. The transducer of claim ll wherein:

said transducer is of the expansion-compression type whereby saidradiator moves with respect to said base in accordance with theelectrical potential across the faces of said crystal.

10. The transducer of claim 4 wherein:

said connection between said stub and said base includes an ultrasonicaccoustic isolator.

11. An ultrasonic transducer for operation at a given ultrasonicfrequency comprising:

a centrally supported curved shallow dish radiator;

a tuning rod having a length of approximately, one half the wavelength,in said rod, of an accoustic wave at said given frequency;

a piezoelectric crystal connected between the center of said radiatorand one end of said rod.

12. The transducer of claim 11 further comprising:

a base for supporting said transducer on an external structure, saidbase being connected to said rod at an accoustic null point along thelength thereof.

13. The transducer of claim 11 further comprising:

a base for supporting said transducer on an external structure, saidbase being connected to said rod at an accoustic null point along thelength thereof.

14. The transducer of claim 11 wherein:

the connection between said base and said rod includes an ultrasonicaccoustic isolator.

15. The transducer of claim 11 wherein:

said crystal has its piezoelectric axis aligned with the axis of saidrod and perpendicular to the surface of said radiator.

1. An ultrasonic transducer comprising: a piezoelectric crystal havingfirst and second electrode faces on opposite sides thereof; aself-supporting shallow dish radiator mounted at its center to the firstface of said crystal to be solely supported thereby; a support membermounted at one end to the second face of said crystal and having itsother end structurally unconnected; a base; and a connecting elementsecured between said support member at an acoustical node in saidsupport member and said base.
 2. The transducer of claim 1 wherein: saidconnecting element includes an ultrasonic acoustic isolator.
 3. Thetransducer of claim 1 additionally including: an electrical switchhaving alternately conducting and nonconducting states mounted on one ofsaid base or said support member and having an actuator contacting theother of said base or support member for changing between said stateswhen said support member and said base move relative to each other,thereby providing a tamper detection means.
 4. A transducer according tocalim 1 for operation at a given ultrasonic frequency wherein: saidsupport member comprises a tuning stub connected at one end to saidsecond face and aligned perpendicular to said second face, said stubbeing approximately one half the wavelength in said stub of anacoustical wave at said given frequency, and said stub being connectedto said base at the midpoint thereof.
 5. The transducer of claim 1wherein: said radiator has a curved shape presenting one concave and oneconvex surface; and said radiator is mounted to said crystal at thecenter of said concave surface.
 6. The transducer of claim 1 furthercomprising: an impedance transformer mounted to said base having firstand second windings, the leads of said first winding being connected tothe electrode faces of said crystal and the leads of said second windingbeing connectable across the outputs of an ultrasonic frequencytransmitter.
 7. The transducer of claim 1 further comprising: apreamplifier having inputs connected across the electrode faces of saidcrystal; and an impedance transformer mounted to said base having firstand second windings, the leads of said first winding being connected tothe output of said preamplifier and the leads of said second windingbeing connectable across the inputs of an ultrasonic frequency receiver.8. The transducer of claim 1 wherein: said crystal has its piezoelectricaxis oriented perpendicular to said radiator.
 9. The transducer of claim1 wherein: said transducer is of the expansion-compression type wherebysaid radiator moves with respect to said base in accordance with theelectrical potential across the faces of said crystal.
 10. Thetransducer of claim 4 wherein: said connection between said stub andsaid base includes an ultrasonic accoustic isolator.
 11. An ultrasonictransducer for operation at a given ultrasonic frequency comprising: acentrally supported curved shallow dish radiator; a tuning rod having alength of approximately, one-half the wavelength, in said rod, of anaccoustic wave at said given frequency; a piezoelectric crystalconnected between the center of said radiator and one end of said rod.12. The transducer of claim 11 further comprising: a base for supportingsaid transducer on an external structure, said base being connected tosaid rod at an accoustic null point along the length thereof.
 13. Thetransducer of claim 11 further comprising: a base for supporting saidtransducer on an external structure, said base being connected to saidrod at an accoustic null point along the length thereof.
 14. Thetransducer of claim 11 wherein: the connection between said base andsaid rod includes an ultrasonic accoustic isolator.
 15. The transducerof claim 11 wherein: said crystal has its piezoelectric axis alignedwith the axis of said rod and perpendicular to the surface of saidradiator.